Proportions are somewhat questionable: roof tiles are too large (what is their material) and the house would be too small for living, especially contrasting with huge door. Stones under the window look somewhat flat. The stone before the door has somewhat sharp top edge. Finally, where is the light source?

I'd say for a first outing this is pretty darn good work!

My only critique would be that the grass seems to have a slightly higher level of detail than the rest of the image.  I don't know if that makes sense, but where most of the image has kind of a graphic novel look to it, the grass looks like it could come right out of a modern 3D game.  

It looks good, however i cannot imagine how the lowest middle plate of the roof could bend like that... Atleast not if its a normal building materal (not chocolate or something funny)

Here is some art i did favorite:

http://opengameart.org/content/orange-scifi-buildings-for-isometric-games